In performing maintenance, inspections and other work related to pipelines, it is often desirable to plug the pipeline to prevent (or control) flow through a section thereof. Examples of pipelines which require plugs to be used therein include sewer pipelines, water delivery pipelines and pipelines for delivery of various gases and liquids. Prior art pipe plugs generally include a cylindrical plug formed of rubber or other elastic materials which are provided with sufficient thickness and selected from appropriate materials to exhibit high strength but still maintaining elasticity. The plug has a hollow interior to which a source of compressed gas is connected.
The plug is positioned where desired within the pipeline and then compressed air is fed to an interior of the plug. The plug expands under this internal pressure until an outer wall of the plug expands and comes into contact with the inner diameter of the pipeline. By adding additional pressure, engagement between the plug and the inner wall of the pipeline can be increased so that the plug will resist movement. Generally, this resistance to movement is dependent upon the coefficient of friction between the inner wall of the pipeline and the outer wall of the plug as well as the force exerted laterally by the plug upon the pipeline inner wall, generally correlating with the pressure within the plug.
Typically, such plugs can only handle a pipeline pressure outside of the plug of 15 to 25 psi before the plug will begin to move within the pipeline. As it is often necessary for pressures greater than this to be withstood by the plug, various restrains are known to hold the plug in place and to assist in resisting this pipeline pressure. Installment of such restraints adds to the complexity of the plug installation process. Accordingly, a need exists for a pipeline plug which is highly resistant to movement under pipeline pressure applied to the plug, so that such blocking or other restraint can be avoided while still maintaining the plug positioned where desired.